BUCHANAN, N.Y. – A buildup of combustible gases inside a transformer that routes electricity from Indian Point Unit 3 to the grid, essentially shut down the plant just after 1 a.m. Wednesday morning. The plant stopped sending power to the grid about 4:30 a.m.
During routine maintenance operators discovered a buildup of combustible gases inside the oil of the transformer; a buildup of this kind can indicate transformer degradation. The plant is running at about 13 percent power at this point, according to officials at the Nuclear Regulatory Commission.
The company’s plan is to “tag out,” or remove from service, the affected auxiliary transformer and temporarily supply all plant busses, which are electrical distribution systems for plant safety systems, from another auxiliary transformer.
An NRC inspector assigned to Indian Point Unit 3 was at the plant overnight to monitor the down power, and Entergy’s approach to dealing with the auxiliary transformer issue. NRC officials said the inspector did not identify any immediate safety concerns. Neil Sheehan, spokesperson for the NRC said there is not a set date when IP3 will return to full operation.
During the powering down, operators dump steam generated by super-heated water directly into the plant’s condenser.
This is instead of the normal processes of Indian Point pressurized water reactor system, which during regular operation routes super-heated steam through a turbine, which generates electricity. During normal operation the steam is pumped over pipes containing cool Hudson River water, which turn the super-heated steam back into water to be heated again in the system, much like a car’s radiator.
Sheehan said it’s unclear if this down-power will count against the plant’s performance indicator for unplanned down-powers. Since 2007, not including Wednesday morning’s incident, Indian Point Unit 3 has had nine unplanned down powers or plant shut downs for various reasons since January 2007, according to officials at the NRC.